But now, more than a decade later, two research groups in the United States and one in Britain each believes it has nearly enough data to begin clinical trials for a new technique based on the transfer of mitochondria — only in this case, researchers want to pair the nuclear DNA of one egg with all the mitochondria of another. Their aim is not to cure infertility. Rather, they hope to prevent a variety of devastating diseases caused by mutations in mtDNA. The new technique, which they call mitochondrial-replacement therapy, is far more advanced than the cytoplasm injection — and the researchers have studied the procedure’s impact on animals and human cells up to a pivotal point: They have created what appear to be viable three-parent embryos. They have yet to implant one in a woman, though. In Britain, national law prohibits altering the germ line, but Parliament is very likely to vote later this year on whether to allow mitochondrial replacement to move forward. Likewise, this February, the F.D.A. held a meeting to examine the possibility of allowing clinical trials. If either gives the go-ahead, it will be the first time a government body expressly approves a medical procedure that combines genetic material of three people in a heritable way. The historic nature of the moment has turned the technique into a symbol, a red line separating humanity from a dystopian or progressive future, depending on how you look at it. In the months leading up to the meeting, the F.D.A. received several hundred emails from members of the public objecting to the idea of three-parent embryos on grounds that included: “It’s bizarre”; “You are walking in Hitler’s footsteps if you allow this”; and “We will have a world of mad scientists.”
As the scientists who were pressing for mitochondrial replacement kept pointing out, these fears were somewhat unfounded. It cannot allow people to design babies to their specifications — in fact, it comes with most of the same risks and uncertainties that attend old-fashioned reproduction. It’s hard not to wonder if the argument is really about the technique or the sacrosanctity of DNA. Is our fear of crossing the germ line causing us to block a technology that could improve people’s lives, and if so, is the fear itself a thing we should also be afraid of?
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